Effect of Blending Silica Fume and GGBS on Chloride Penetration in Concrete under Temperature Gradient Conditions

This paper investigates the significance of thermal diffusion on chloride diffusion in concrete under high ambient temperature in arid climates. Of particular interest is to study the effects of silica fume (SF) and ground granulated blast furnace slag (GGBS) on chloride penetration into concrete subjected to temperature gradient conditions. This was achieved by making three sets of concrete samples—the control samples, the samples containing 5% SF, and the samples containing 5% SF and 50% GGBS. These samples were exposed to a NaCl environment under isothermal and thermal gradient conditions. The total and free chloride contents of the exposed samples were determined via potentiometric titration. The total chloride concentration of the samples exposed to thermal gradient conditions could be 1.3–6 times higher than those exposed to isothermal conditions at the same temperature. The addition of SF and GGBS yielded significantly lower total and free chloride contents than the control samples under isothermal and thermal gradient conditions. While thermal gradient significantly reduces the chloride binding capacity, adding SF and GGBS increases this ability. SEM analysis revealed microstructural changes in concrete due to high temperature and thermal gradients, with larger and deeper pores in samples exposed to thermal gradient. Numerical estimation of chloride concentration and the corrosion initiation time of a reactor containment building was also performed using the modified chloride diffusion equation, including the effects of mass- and thermo-diffusion.